1. Field of the Invention
The present invention relates to a thermal transfer foil and a method of forming a phosphor screen by using a thermal transfer foil for use in cathode ray tubes such as transmissive type flat cathode ray tubes in which a phosphor screen is formed on a screen panel side.
2. Description of the Prior Art
There is known a reflection type flat cathode ray tube whose flat glass tubes envelope is formed of a triple comprising a screen panel, a front panel and a funnel portion having a neck portion. That is, the flat glass tube envelope comprises the screen panel and the front panel that are bonded by frit glass in an opposing relation so as to form a flat space therebetween, a funnel portion bonded and sealed on one side of the screen panel and the front panel similarly by frit glass and the neck portion welded to the funnel portion at the funnel portion's small diameter open end. An electron gun is disposed within the neck portion.
On the inner surface of the screen panel, there is deposited a phosphor screen through a reflection film made by vapor deposition of aluminum material or the like. An electron beam emitted from the electron gun is scanned on the phosphor screen in the horizontal and vertical directions. An optical image that is excited and rendered luminous by the electron beam can be viewed by the viewer from the front panel side opposing the screen panel.
Recently, there has been developed a transmissive type flat cathode ray tube having a triple structure that comprises a screen panel, a back panel and a funnel portion having a neck portion.
In this case, a phosphor layer is formed on the inner surface of the screen panel and an aluminum layer must be further formed on the phosphor layer as a metal-backing layer. The reason for this is that a high voltage is applied to the phosphor screen and brightness and contrast must be improved.
As a method of forming such phosphor screen, a phosphor layer is formed by a slurry method or electrodeposition method, an acrylic resin layer is formed on the phosphor layer by a lacquer method as an intermediate layer and an aluminum layer is formed on this acrylic resin layer by a vacuum evaporation method.
This method, however, requires much more processing, thus the manufacturing cost of the phosphor screen cannot be reduced substantially. Also, the film thickness of the phosphor screen cannot be kept constant.
Furthermore, the aforesaid conventional method needs the intermediate layer. There is then the disadvantage that the aluminum layer may be stripped in the baking process or that a satisfactory mirror surface cannot be obtained.